As is known, when packaging integrated circuits (IC), multiple semiconductor dies are arranged on a single substrate. The silicon dies are first bonded to paddles of the substrate or leadframe by a die bonder, interconnecting wires are wire bonded between the dies and conductors on the substrate. Alternatively, flip-chip processes can be used to flip a semiconductor die over and attach the pads on the dies directly to the conductors on the substrate. The dies on the substrate are then packaged, such as by encapsulation in mold compound, and the molded substrate is then cut to produce a number of singulated semiconductor packages, each having a die encapsulated therein. The process of cutting up the molded substrate is often referred to as singulation.
Typically, the molded substrate is singulated using one or more rotating dicing saws that cut the molded substrate first along an X axis, and then along a Y axis. A saw jig with an applied vacuum force, holds the molded substrate against a rubber pad, prior to and, during singulation, and the vacuum also holds the singulated semiconductor packages on the rubber pad after singulation.
As semiconductor dies shrink in size, semiconductor packages have also been reducing in size, an example of which is the Quad Flat No-lead (QFN) semiconductor package. When the rotating saw is employed to singulate QFN packages from a molded substrate, several difficulties arise in relation to securing the molded substrate and singulated QFN packages during and after singulation, and in relation to the quality of the cut that is obtained.
The rotating saw is a contact cutting process, which exerts considerable lateral forces on the molded substrate during cutting. The vacuum force on the molded substrate, and indeed on each of the individual packaged semiconductor dies, must be greater than the lateral force to prevent the individual packaged semiconductor dies from moving, or worst yet, from being thrown off the saw jig.
When the size of the individual packaged semiconductor die is reduced, the holding force on it also reduces, however the lateral force during cutting remains substantially the same, which compounds the difficulty in securing the individual packaged semiconductor dies. Hence, a disadvantage of the rotating saw is the difficulty in securing the individual packaged semiconductor dies during cutting.
As saw cutting is a contact process, the molded substrate and the resultant singulated packaged semiconductor dies are subjected to considerable mechanical forces during cutting. Hence, another disadvantage of using the rotating sawing, is the risk of damage to the dies in the singulated semiconductor packages, which can adversely affect reliability.
Some semiconductor packages, such as the QFN package, include copper portions, which are thicker than the copper portions in other types of semiconductor package, such as a ball grid array (BGA) package. The thicker copper portions are both more difficult to cut through, and smear and burr on the semiconductor packages when the rotating saw is used for singulation.
Hence, another disadvantage of using the rotating saw is the difficulty in cutting through the copper portions, without smearing and burring on the individual packaged semiconductor dies.
One alternative to sawing is laser singulation, which is a non-contact process. A laser beam cuts the molded substrate by burning and evaporating material from the substrate. However, the wavelength of the laser beam is selected by the object material, and for composite material like the molded substrate with copper and mold compound, the laser absorbing rates for copper and mold compound are very different. Therefore, a disadvantage of laser singulation is that it is difficult for the energy from the laser beam to be efficiently absorbed by both the copper and mold compound, and thus, it is difficult for the laser beam to cut through the package material.
Another method of singulating semiconductor packages employs a water jet to cut the molded substrate. Water jet cutting is a non-contact process, which uses a jet of water to cut through the molded substrate. The jet of water comprises a stream of extremely high pressure water with an entrained stream of abrasive particles. Water jet cutting is cool, and possesses a low risk of heat and mechanical damage to both the molded substrate and the resultant singulated semiconductor packages. In addition, there are limited restrictions on the material that can be cut by a water jet. Further, as the cutting force is perpendicular to the surface of the molded substrate, there is little resultant lateral force on the molded substrate and the resultant singulated semiconductor packages. Hence, the force required to secure the singulated semiconductor packages is lower than that in sawing. In addition, the cutting quality of the water jet is good and stable, with no burring and smearing.
Unlike the sawing or laser cutting which use one vacuum jig for securing the molded substrate during cutting, a prior art water jet handler uses two vacuum jigs to hold the molded substrate. This is because the extremely high pressure of the water jet cuts through almost any material within about 300 mm from the nozzle that provides the water jet. Consequently, there is a need to ensure a certain amount of clearance or relief for the water jet, behind the molded substrate.
The prior art water jet handler has a movable chuck table with two vacuum jigs, one with relief slots in the X direction, and the other with relief slots in the Y direction. The chuck table can move in the X and Y directions, and can rotate about a vertical axis, which is parallel to the water jet. Rotation about a vertical axis is often referred to as displacement in the theta direction. All the movements of the chuck table is relative to the position of the water jet nozzle.
With reference to FIG. 1, a molded substrate for singulation is loaded onto a first vacuum jig at a loading location, and secured to the first vacuum jig by an applied vacuum. The chuck table then moves the first vacuum jig to a cutting location below the nozzle of the water jet, where a vision system operates with the chuck table to align the molded substrate with a cutting line of the water jet system. The molded substrate is then cut in the X direction as the chuck table transports the molded substrate transversely across the water jet in the X direction. For multiple cuts in the X direction, the operation as described is repeated. Next, the molded substrate, which has been cut in the X direction, is transferred from the first vacuum jig onto a second vacuum jig, and secured by an applied vacuum. A second vision alignment is performed, and the molded substrate is cut in the Y direction, as the chuck table transports the molded substrate transversely across the water jet. This operation is repeated for each cut in the Y direction. The individual packaged semiconductor dies are now individually held on the second vacuum jig, and the chuck table moves the second vacuum jig to the loading location, where the individual packaged semiconductor dies are unloaded. This process is repeated for each molded substrate.
A disadvantage of the prior art water jet handler is low efficiency, as only one molded substrate is sequentially processed at a time by the handler, and actual cutting of the molded substrate is performed for only part of the sequential process. Hence, the throughput of the handler is low.
In addition, as the prior art water jet handler loads a molded substrate and unloads the singulated molded substrate at the same loading/unloading location, the prior art water jet handler is not suited for integration with in-line manufacturing operations, where equipment are arranged in sequence. In addition, the low throughput of the handler will adversely affect the throughput of the in-line manufacturing operations.